Electronic Power Control

Electronic Power Control

What Does the Electronic Power Control (EPC) Warning Light Mean?

Traditionally hand brake, accelerator pedal, clutch and bonnet release, used some sort of cable system and the steering column and gear levers used several mechanical linkages. Today virtually all these mechanical systems have been replaced by electronics in the form of sensors, feeding computers and electric motors performing as actuators. The legacy accelerator cable that controlled the throttle valve and fuel supply in the trusty old carbureter has been entirely replaced by electronics. It is now referred to as drive-by-wire (drive the car by means of electric wire control) and the EPC circuit oversees drive-by-wire system.

So what is an EPC circuit?

EPC stands for Electronic Power Control (EPC) and is a sub circuit of the car's computerized engine management system better know as its ECU which stands for Electronic Control Unit or  Engine control Unit. The EPC circuit uses the input signal supplied by the accelerator position senders and  the throttle angle senders to calculates how much engine power the driver requires. The EPC system also receives input signals from other systems on the car, like the stability and cruise control systems and translates this data into engine torque by means of the actuators.

The EPC circuit also monitors these components at start up and whilst driving and should it detect any malfunction, it will readily illuminate the EPC warning light . The EPC light is a bright yellow/amber instrument cluster light displaying the letters EPC. But it's just a 'Indicator Symbol light' that  informs the driver that an issue occurred in the torque system. Some faults within the EPC circuit will more than likely disable other functions on your vehicle that may even cause it to go into limp mode and not rev or perform very sluggishly.

EPC Warning Light

Since the EPC is a sub circuit of the ECU which supervisors several other systems on the vehicle, it is likely that other warning lights my also illuminate  on the instrument cluster. For example the Check Engine Light (CEL) may illuminate to indicate that the engine itself isn’t operating at normal efficiency. At the same time the stability and cruise control will be disabled and their respective lights may turn on as well.  

When this happens, you will need to have your car scanned for diagnostic trouble codes (DTC) or you could do it yourself if you have an appropriate scanner. Once the error codes are identified, it would be relatively easy to repair / replace the component responsible, and thereafter clear the fault codes. The illuminated lights should all turn off and the car should once again drive as per normal.

Is it safe to drive with the EPC light on?

Many people inquire  whether or not it safe to drive with the EPC light on? In my humble opinion, I would say,  Yes it is safe to drive with the EPC light on, because the EPC light is an abler light and not a red light. Red lights dictates that you shouldn't  drive the car at all, until the problem causing the red light to illuminate is repaired. Whereas an amber light is just an information sign. One can equate dashboard lights to road signs, for example if a red traffic light or a red stop sign with white-background  or other red and white regulatory sign is blatantly disobeyed, it will more likely than not result in harm or injury. Round red and triangular red road signs are warning signs and means danger. Also any sign with a white background signifies the sign is permanent  whereas a sign with a yellow background signifies that the sign is temporary and any square /diamond shaped orange/amber signs are used for roadway works information and guidance.

So return to the subject at hand, yellow/amber lights are therefore informative and temporary. However when the EPC light is on and the car goes into limp mode then its not safe to drive with the EPC light on, because you will be going dead slow and be an obstruction to other motorists. Limp mode is just a shortened form for limp home mode which is  an operating mode set by the vehicle's on-board  computer which is pre-programmed by the manufacturer. This program limits  your vehicle throttle in order to protect the engine or the car itself or its occupants from harm or injury and the car should only be driven to take it for  repairs.

As can be seen, the four signs on the right are red with the top two including white
whereas the four signs on the left are all yellow  which is informative and temporary. 

However the severity of the EPC problem can vary greatly and the vehicle may not be operable at all.  Common cause of  car’s EPC circuit malfunctioning are its sensors. Replacement normally solves the problem, however EPC faults can register intermittently to the point of frustration. In such cases it's very likely the wiring harness are intermittently faulty especially where the plugs connect to the sensors. If your engine suddenly shuts off while driving, you may want to look at the Engine speed sensor. The  crank shaft rotation sensor also commonly fail, when starting the car's engine while stationary. A tell tale sin is that the  the engine switches off after two second of idling. 

The brake light switch is yet another  EPC light trigger and is solved by replacement. This switch is a double pole double trow switch and isn't physically associated with the brake other than the same switch is used. On automatic vehicles brake switch failure locks the gear lever in Park and prevents  from selecting any other gear. The Mass air flow sensor is another common cause of EPC problems but in many cases it's not the MAF itself. It may be due to minor cracks in the rubber hoses that causes air to be sucked in, upsetting ECU calculations. The Throttle body and its angle sensors and drive motor is another is also another EPC problem child.

@volkswagenindia why am I getting EPC light again and again. Already 7 times repaired. Tired!! @Volkswagen pic.twitter.com/S1GzM6shNT

— विरल (@Viral_HS1) July 1, 2017